1. Field of the Invention
This invention relates to a magnetic disc cartridge which comprises a large capacity magnetic disc contained in a casing and is used in a magnetic recording and reproduction in which the magnetic disc is rotated at high speed, and more particularly to such a magnetic disc cartridge in which the magnetic disc can be surely chucked by a spindle for rotating the disc.
2. Description of the Related Art
There has been known a magnetic disc, a so-called floppy disc, which comprises magnetic layers formed on opposite sides of a flexible disc base of a polyester sheet or the like. Information is recorded on the floppy disc by a magnetic head while rotating the floppy disc. Such floppy discs have been mainly used as recording media for computers because they are easy to handle and available at low cost.
Recently the magnetic disc of this type is generally held for rotation in a small hard casing and used in the form of a magnetic disc cartridge as represented by a 3.5-inch floppy disc.
In the magnetic disc cartridge having a hard casing, the casing is provided with a magnetic head insertion opening through which a magnetic head is inserted into the casing and a shutter member for opening and closing the opening. The casing is further provided with a spindle hole in the bottom thereof and a spindle is inserted through the spindle hole to rotate the magnetic disc holding a center core fixed to the center of the magnetic disc. There has been constant demand for a magnetic disc cartridge having a larger storage capacity.
When a magnetic disc cartridge larger than conventional magnetic disc cartridges in storage capacity is developed, a novel disc drive system for driving the magnetic disc cartridge having a larger storage capacity is provided. Such a novel disc drive system is generally arranged to be able to drive magnetic disc cartridges having smaller storage capacities as well as the newly developed larger capacity magnetic disc cartridge. Such capability of driving magnetic disc cartridges having smaller storage capacities as well as the newly developed larger capacity magnetic disc cartridge will be referred to as "downward compatibilities", hereinbelow.
In order to obtain such downward compatibilities, the disc drive system should be arranged to be able to drive both the larger capacity magnetic disc cartridge and the smaller capacity magnetic disc cartridge by the same mechanism.
In the larger capacity magnetic disc cartridge, the magnetic disc is rotated at a higher speed than in the smaller capacity magnetic disc cartridge.
In the conventional (smaller capacity) magnetic disc cartridge, the center core of the magnetic disc is provided at the center thereof with a center hole into which a spindle of the disc drive system is inserted, and a drive pin hole with which a drive pin on the spindle of the disc drive system is engaged is formed in the center core radially spaced from the center hole. When the conventional magnetic disc cartridge is loaded in a disc drive system, the spindle of the disc drive system is inserted into the center hole of the center core with the center core urged toward the spindle under magnetic attraction. However the drive pin of the disc drive system cannot be generally brought into engagement with the drive pin hole by only loading the magnetic disc cartridge and is brought into engagement with the drive pin hole while the spindle rotates (the drive pin is rotated together with the spindle) relative to the magnetic disc. When the drive pin is brought into engagement with the drive pin hole, the magnetic disc is chucked and comes to be rotated in response to rotation of the spindle and the drive pin. That is, it is necessary for the spindle and the drive pin to rotate relative to the magnetic disc or the center core thereof in order to chuck the magnetic disc.
In the case of the conventional small capacity magnetic disc cartridge, there acts resistance to rotation of the magnetic disc due to its structure as will be described later and accordingly when the spindle begins to rotate, the spindle and the drive pin can rotate relative to the magnetic disc until the drive pin is brought into engagement with the drive pin hole. However in the case of the larger capacity magnetic disc cartridge, the resistance to rotation of the magnetic disc is made very small in order to rotate the magnetic disc at a high speed and accordingly, when the spindle begins to rotate, the magnetic disc can rotate together with the spindle, which prevents the drive pin from being brought into engagement with the drive pin hole and causes chucking failure.
Specifically, in the small capacity magnetic disc cartridge, a cleaning member (liner) is disposed between each side of the magnetic disc and the inner surface of the casing and is pressed against the magnetic disc by a lifter in order to clean the magnetic disc and to support the magnetic disc against the magnetic head to ensure a good head touch. The friction between the magnetic disc and the cleaning member resists rotation of the magnetic disc and the drive pin can rotate relative to the magnetic disc and be brought into engagement with the drive pin hole.
To the contrast, in the case of the larger capacity magnetic disc cartridge, the magnetic disc is rotated at a high speed since a high recording density and a high transfer rate are required. For example, the rotational speed of the magnetic disc is 300 to 360 rpm in the small capacity magnetic disc cartridge and 3000 to 3600 rpm in the larger capacity magnetic disc cartridge. When rotating at such a high speed, the driving resistance of the magnetic disc should be as small as possible, and accordingly the conventional cleaning system comprising a cleaning member and a lifter for pressing the cleaning member against the magnetic disc is not suitable for the larger capacity magnetic disc cartridge. As described above, the spindle, the drive pin and the center core should be the same as those in the conventional magnetic disc cartridge for the purpose of the downward compatibilities. However in the case of the larger capacity magnetic disc cartridge, there is a fear that the drive pin cannot be brought into engagement with the drive pin hole and chucking failure can take place due to small resistance. When the magnetic disc is rotated in the chucking failure state, reliability of recording and reproduction at a high recording density and a high track density cannot be ensured.